However, there is no known gravity dual to QCD, the duality between the \(\mathcal {N} = 4\, SU(N_c)\)  super-Yang-Mills theory and type IIB string theory on \(AdS_5 \times S^5\)  is the most studied example in the context of AdS/CFT correspondence [1]}, [2]}, [3]} which provided promising results. For example, the ratio of shear viscosity over entropy density obtained from this duality, \(\eta /s = 1/4\pi \)  [4]}, [5]}, [6]} is consistent with the experimental data [7]}.
